It is well known in the art of geophysical surveying that analysis of resistivity and induced polarization data can provide useful information regarding subsurface structures and materials, including the possible presence of mineralization commonly associated with commercially valuable ore bodies. When electrical current is applied to the ground, variations in the subsurface can impact current flow and affect the distribution of electric potential, such that measurement of potential at the surface can provide information regarding the subsurface.
Conventional practice involves the use of a first pair of spaced-apart electrodes to pass current into the ground, and the resulting potential drop between a second pair of electrodes is measured. Resistivity and induced polarization effects have been used for many years to interpret the subsurface.
Early systems employed an analogue meter measuring a first dipole while current was transmitted into the ground using a second dipole, with data being transcribed by hand. Digital equipment became available in the 1980s and voltage data could thus be subjected to digitization and recorded to storage media. In a significant development, multi-channel measurement instruments allowed for simultaneous measurement of multiple dipoles (see FIG. 1a), and ultimately the practice moved to the use of multiple multi-channel measurement instruments in what is commonly referred to as a distributed array (see FIG. 1b).
While each development within the art increased the amount of data that could be collected and used for surveying purposes, the increased complexity dramatically increased the number of wires, the number of electrical connections, the setup complexity, and the size of the crew required to implement the system. As many exploration survey activities take place in relatively remote locales with restricted access and mobility within the areas, increases in complexity, equipment and crew sizes results in substantial cost increases and increased potential for crew injury.
In addition, one of the primary sources of noise in resistivity and induced polarization surveys is what is commonly known as “cross talk”. Cross talk occurs where a signal from one conductor wire in the system interferes with the signal in an adjacent wire through inductive, capacitive or galvanic means. For example, signals from a current wire (part of the current transmission subsystem) may interfere with signals in the potential wire (part of the data collection subsystem). This problem is exacerbated as the systems become more complex and increase the number of wires employed for signal transmission.
What is needed, therefore, is a system and method for collecting geophysical data that reduces complexity and measurement noise.